Traditionally, high-current electronic applications such as electric motor drive controllers require the use of large electronic components to handle the current. These components are not only physically large, but also generate a high amount of heat, and are often sold and mounted as through-hole devices (devices which must be mounted through holes in the circuit board and may need to be hand-soldered in place.) Through-hole devices cannot be easily mounted by automated methods such as pick-and-place machines, and require manual placement, which increases the manufacturing expense of the module. Even in applications where through-hole devices are replaced with easier to place surface mount devices, the assembly of the power devices, heat sink, bus capacitors, bus structure, external power connectors, signal interconnect, and enclosure requires a great deal of labor and multiple processes.
To deal with heat issues, a typical high-power application uses Insulated Metal Substrate Technology (also referred to as “IMST”), which bonds a circuit board to a flat metal plate to try to increase heat conduction away from the electronics. In order to dissipate more heat, the surface area of the plate must be increased (typically done by using a finned heat sink attached to the metal plate) or by using other technologies such as liquid-cooling to remove heat.
The Bergquist Company (http://www.bergquistcompany.com/ts_thermal_clad.cfm) manufactures thermally conductive interface materials using the IMST technology discussed above. A dielectric layer with minimal thermal resistance bonds a metal base layer to a circuit foil layer. A disadvantage of IMST is that the circuit and dielectric layers are bonded to a thin metal plate during the manufacturing process. While this thin metal plate provides some heat conduction, the only way to increase the heat conduction ability is to make the plate larger (wider and longer but still the same thickness), or by attaching it to a separate, larger finned metal heat sink. Small fins may be provided on the bottom of the IMST arrangement by cutting, bending, and/or welding fins on the bottom of an IMST plate. While this helps with the heat dissipation properties, it adds a costly manufacturing process.
Another disadvantage of an IMST approach is that the thermal resistance of the interface between the thin metal plate and the attached finned heat sink is high, which decreases the thermal efficiency.
The assignee of the present invention uses bonding technology similar to IMST in the manufacturing process for its FlexBox™ technology, bonding a flexible circuit to a flat metal plate (or plates)(see U.S. Pat. No. 6,655,017 B1, entitled “Electronic controller unit and method of manufacturing same”). A disadvantage of this type of arrangement is that a thin dielectric layer sandwiched between the circuit layer and the metal base layer must be baked (heat cured) in an oven, which requires an additional manufacturing step.
What is needed in the art is an electrical circuit assembly in which an electrical circuit may be more easily, quickly, and less expensively coupled with a heat sink with improved heat transfer characteristics to the heat sink.